Using a serrated knife or the heel of a chef's knife, chop 12 oz. of the chocolate for the ganache by shaving shards from the bar and then cross-cutting, to get chips now bigger than peanuts. Transfer to a small stainless-steel bowl. Chop the remaining 2 lb. chocolate the same way, and set aside to use for dipping.
Heat the cream in a small saucepan until it just comes to a boil and pour it over the chopped ganache chocolate. Using a wooden spoon, stir quickly in small circles in the center of the bowl. The chocolate center will become a viscous, shiny emulsion.
Gradually stir in larger circles, bringing in more chocolate from the sides. Keep enlarging the shiny center until all the chocolate has been incorporated. If the emulsion cools before all the chocolate has melted, briefly flash the bowl over a pan of hot (not simmering) water for a few seconds, being careful not to overheat the ganache and lose the emulsion. When there are no more lumps, continue stirring for one more minute; don't overmix. Set the ganache aside to cool.
Meanwhile, in another bowl, beat the butter with a wooden spoon until it's very soft, smooth, and creamy. When the ganache has cooled to room temperature and thickened noticeably, add the butter, in small pieces a few at a time. The butter should blend without melting. Stir until no butter bits remain. Gradually pour in the liquer, stirring constantly to maintain the smooth emulsion.
If you want to pipe the truffles immediately, chill the ganache in the refrigerator until it's cool but not firm, 10 to 15 minutes. Otherwise, cover the bowl with plastic wrap and let it sit at room temperature until ready, up to one day. When you're ready to pipe, the ganache should be as smooth and as soft as peanut butter (but not as sticky).
If you're tempering the chocolate, continue heating it over the pan of hot water until a chocolate thermometer registers between 120° and 125° F. Remove the bowl from the saucepan, dry the bottom, and cool the chocolate to 86° F by adding the reserved finely chopped chocolate, 2 Tbs. at a time, stirring after each addition until the pieces melt.
When the temperature reaches 86° F and the pieces no longer melt (you might not use all the finely chopped chocolate), very gently raise the temperature to between 88° and 91° F by flashing the bowl over the pan of hot water for 10 seconds at a time, drying the bottom of the bowl every time.
To test if the chocolate is in temper, spread a bit on a swatch of parchment and let it cool for a few minutes. The chocolate is in temper if it sets quickly. If the chocolate has white streaks and is tacky to the touch, it is not in temper; start the process again by heating the chocolate to 120°F.
Keep the chocolate in temper while dipping by holding it between 88° and 91° F. To monitor the temperature, tape the thermometer to the bowl (the bulb shouldn't touch the bowl). If the temperature in the center of the bowl drops to 89° F, flash the bowl over the hot water in 10-second increments until the temperature hits 90° F.
After getting the hang of classic chocolate truffles, you can experiment with other flavors. You can modify the ganache by using another liquer, adding a fruit purée, or steeping herbs in the cream.
To add fruit to the ganache, purée fresh ripe fruit and strain out any fibers or seeds. Try raspberries, mangos, apricots, passionfruit, sour cherries, or any fruit with strong flavors and not too much acidity.
To use herbs, steep them in the hot cream for 20 minutes; then strain them out. Remeasure the cream (The herbs will have absorbed some of the liquid), correct the measurement with more cream, and add it to the chopped chocolate. Try fresh mint, basil, licorice-flavored hyssop, or dried teas like Earl Grey and jasmine.